The present invention relates generally to braking resistors used in power systems during power system disturbances, and more particularly to a new dynamic braking resistor and a method of damping subsequent oscillations on a power system following a power system disturbance using the dynamic braking resistor.
In the past, braking impedances, typically referred to as "braking resistors," have been applied to a few power systems, such as in remote generation locations. A typical braking resistor provides a shunt resistance path to ground when coupled with the power system by switching during a power system disturbance. Such power system disturbances may be caused by a downed power line, a short circuit on a transmission line, a lightening storm, or other undesirable events. These conventional braking resistors have a mechanical switch which couples the resistor to the power system for a predetermined time following the detection of a major system disturbance.
After this predetermined time, the conventional braking resistors are abruptly removed from the line by opening the mechanical switch. After removal from the line, these conventional braking resistors cannot be switched back into the line until they have cooled down sufficiently, which requires from ten minutes up to several hours. Thus, conventional braking resistors are incapable of providing any damping for the subsequent oscillations of the power system which follow the disturbance and the insertion of the braking resistor. Furthermore, the fixed resistance or conductance nature of a conventional braking resistor lacks flexibility and imposes an additional loss burden on the power system during the time it is coupled therewith if less than the total dissipation is required to respond to the disturbance.
Thus a need exists for a dynamic braking resistor, and a method of damping subsequent oscillations on a power system following a power system disturbance, which is directed toward overcoming, and not susceptible to, the above limitations and disadvantages.